No flaps on canards?
Orval R. Fairbairn
: Is there any reason why there are no provisions for flaps on the more popular
: homebuilt canard aircraft?
:
Flaps would add too much pitch down moment to the wing, overcoming
the control authority of the canard.
The size of the canard would have to increase significantly to
overcome the pitch moment.
--
Orval R. Fairbairn Mtn View, CA (415) 969-4351 (h) (408) 756-1473 (ofc)
o...@fagin.msd.lmsc.lockheed.com *
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Mark Y. deLevie
: Yes. Since the wing is located relatively far behind the CG on a canard
: airplane, the large nose-down pitching moment caused by lowering flaps is
: often impossible to trim with a canard. This is one reason why canard
: airplanes make poor short-field airplanes.
Well put. You might ask, "Why not just size the canard so as to be able to
trim out that stronger pitching moment?" The answer lies in the safety
net that the design provides against stalling the main wing: the canard
surface should always stall first. If the canard still has further lifting
capacity, then clearly it isn't stalled. With the wing flaps up, such a
plane could enter main wing stall ==---> disaster.
Mark deLevie (die fliegende Hollander)
Jay Hardin
Carl Stevens (e00680)
Or you would have to put flaps on both the main wing and the canard. Of
course that would entail non symetrical deployment of the flaps* and probably
some type of computing/servo solution.
* Front to back.
At least that's the way I understand it.
--
Carl Stevens _ Long EZ N223MM
cste...@ladc.lockheed.com _\_/^\_/_
My opinions are my own. _____/_/_/|\_\_\_____ 4 Young Eagles Flown
Ted Boudreaux
Mike Thompson
>ted_bo...@hp-pcd.hp.com (Ted Boudreaux) writes:
>: Is there any reason why there are no provisions for flaps on the more popular
>: homebuilt canard aircraft?
>:
> Flaps would add too much pitch down moment to the wing, overcoming
> the control authority of the canard.
>
> The size of the canard would have to increase significantly to
> overcome the pitch moment.
Or the canard could sweep a la the Tomcat (Starship uses this method in
conjunction with flaps).
In normal flight, the canards are swept. When the flaps come down, the canard
sweeps to actually a slight forward sweep, thus increasing the canard lift.
SITYS Dittos! - Mike
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Albert Sykes
: In <412opo$s...@butch.lmsc.lockheed.com>, orf@fagin (Orval R. Fairbairn) writes:
: >ted_bo...@hp-pcd.hp.com (Ted Boudreaux) writes:
: >: Is there any reason why there are no provisions for flaps on the more popular
: >: homebuilt canard aircraft?
: >:
: > Flaps would add too much pitch down moment to the wing, overcoming
: > the control authority of the canard.
: >
: > The size of the canard would have to increase significantly to
: > overcome the pitch moment.
: Or the canard could sweep a la the Tomcat (Starship uses this method in
: conjunction with flaps).
: In normal flight, the canards are swept. When the flaps come down, the canard
: sweeps to actually a slight forward sweep, thus increasing the canard lift.
: SITYS Dittos! - Mike
It also changes the length of the moment arm. Pretty clever solution.
Tallyho !
Alpha Kilo
Roger Bleier
: Well put. You might ask, "Why not just size the canard so as to be able to
: trim out that stronger pitching moment?" The answer lies in the safety
: net that the design provides against stalling the main wing: the canard
: surface should always stall first. If the canard still has further lifting
: capacity, then clearly it isn't stalled. With the wing flaps up, such a
: plane could enter main wing stall ==---> disaster.
: Mark deLevie (die fliegende Hollander)
Burt Rutan put together a STOL canard design called the Grizzly.
It had 4 Fowler flaps: 2 on the wings, 2 on the canard.
They were serious flaps extending for 55% of the
chord. Possibly he got around the pitch problem by using the 4 flaps.
There was even a proposal made to put the Griz on amphibious floats!
It was flying in 1982.
--
Roger Bleier
tn...@acad1.alaska.edu
Sitka, Alaska
Peter Duniho
>
>The noteable Orval R. Fairbairn (orf@fagin) wrote:
>::Is there any reason why there are no provisions for flaps on the more
>:: popular homebuilt canard aircraft?
>::
>: Flaps would add too much pitch down moment to the wing, overcoming
>: the control authority of the canard.
>:
>
>course that would entail non symetrical deployment of the flaps* and probably
>some type of computing/servo solution.
>
>* Front to back.
I'm pretty sure I've actually read of a canard design that does this.
Maybe the Beech Starship? It seems that the smaller plane designs
simply accept a somewhat higher landing speed (and after all, this
isn't the only reason canards land fast...there are other reasons that
canard authority is intentionally reduced, preventing really slow
landings), presumably because the added complexity just isn't worth
it. It makes sense to me that on something like the Starship, you get
a good enough improvement, and also complexity on that airplane is
less of a departure from the design than with simpler planes.
-------------------
Peter Duniho N1404Y, Lake Renegade
pe...@microsoft.com PP-ASEL&S-IR
Redmond, WA "Please, take my advice...I'm not using it anyway"
man...@ibm.net
>Is there any reason why there are no provisions for flaps on the more popular
>homebuilt canard aircraft?
>
I think the main reason is that most of the current canard designs basically copy
the original Rutan designed Vari or Long EZ. The "keep it simple" idea has
obviously prevailed here. To date, I don't think there is a molded wing on a
canard, Berkut, Velocity etc.
Forgive my ignorance here but, would'nt it be simpler to maybe modify the
aileron mechanism to offset the neutral deflection position and effectively
work as both flaps and ailerons? This way the mechanism could be kept
beautifully simple like it is now, but yet serve to increase camber at approach
speeds. I can envision a very simple mechanism to do this right now.
I welcome technical responses on this one please.
-- Sidney Rhodes, LongEZ 19SH
Jim Collie
>Burt Rutan put together a STOL canard design called the Grizzly.
>It had 4 Fowler flaps: 2 on the wings, 2 on the canard.
>They were serious flaps extending for 55% of the
>chord. Possibly he got around the pitch problem by using the 4 flaps.
>There was even a proposal made to put the Griz on amphibious floats!
>It was flying in 1982.
>--
>Roger Bleier
>tn...@acad1.alaska.edu
>Sitka, Alaska
The Grizzly, if memory serves me, was of the three-surface configuration, with a
horizontal tail as well as the forward surface. This gives (literally) infinite
more options for loading the surfaces. With a pure Canard and a given CG location,
you have one possible load distribution between the forward and aft wing. With
three surfaces, you have an infinite number of options. If you lower the flaps on
the canard, simply lower the "elevator" to counter the pitch up moment.
Jim Collie
Aeronautical Consulting
John R. Johnson
mechanism, while not terribly complex, is not simple. It poses some
problems with control surface rigidity and gives a serious exposure to
flutter problems.
The real problems with flaps on canard designs results from the very
narrow envelope given by that configuration for safe flight. For example,
if the rear surface should stall before the forward surface, it is very
difficult to get it unstalled. If the forward surface stalls abruptly, the
resulting pitchdown can be unnerving at best. Recall the problems with
paint trim, bugs, and raindrops causing flow over the forward surface to
break laminarity and cause pitchdown. There are also some conditions,
where you can set up a stable, flat, high rate descent, that can not be
broken by control movements. I recall a Cirrus getting in this condition
and continueing to an impact with water.
Also recall the Piper canard prototype that got into an unusual attitude
configuration and crashed fatally with Mr. Piper.
I can rember Burt Rutan, with a large scale model of his Vari-Viggen mounted
on the hood on an old beater car running up and down the runways at St.
Charles, MO, back when he worked for MDC, doing poor man's windtunnel tests
to get the configuration worked into a safe range. Canard designs have many
advantageous features and can be very desireable airplanes. However, Canard
design is NOT something to be undertaken by the old "eyeball" process.
It have been said that "if it looks like an airplane" it will probably fly.
This is pretty much true for conventional designs. They may not fly WELL,
but they will likely fly.
I would think long and hard and get major advice from someone with experience,
like Burt Rutan, before I would consider ANY kind of flap arrangement for a
canard. Not that it can't be done, it can. Just not something you can do
without a lot of thought and some serious testing.
John
Randy Smith
>Mark Y. deLevie (mdel...@wam.umd.edu) wrote:
>
>: Well put. You might ask, "Why not just size the canard so as to be able to
>: trim out that stronger pitching moment?" The answer lies in the safety
>: net that the design provides against stalling the main wing: the canard
>: surface should always stall first. If the canard still has further lifting
>: capacity, then clearly it isn't stalled. With the wing flaps up, such a
>: plane could enter main wing stall ==---> disaster.
>
>: Mark deLevie (die fliegende Hollander)
>
>It had 4 Fowler flaps: 2 on the wings, 2 on the canard.
>They were serious flaps extending for 55% of the
>chord. Possibly he got around the pitch problem by using the 4 flaps.
>There was even a proposal made to put the Griz on amphibious floats!
>It was flying in 1982.
>--
>Roger Bleier
>tn...@acad1.alaska.edu
>Sitka, Alaska
Do Leading edge slats have the same effect of generating the pitching moment
that the canard can't handle? What about leading edge slats on the canard
as well?
I always thought the pitching moment was when the pitcher decided NOT to
throw to first. :-)
-Randy
--
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AT&T Randy...@ColumbiaSC.attgis.com -(X)-
Global Support Center Voice 803-939-7648, V+ 633-7648 ___o/o\o___
West Columbia, SC 29170 "I am the way, the truth, and the life..." -JC
Mark Brian Muller
[discussion of flaps on canards deleted]
>Do Leading edge slats have the same effect of generating the pitching moment
>that the canard can't handle? What about leading edge slats on the canard
>as well?
Yes and no - leading edge slats mainly allow the wing to go to a higher
angle of attack before stalling, thus generating more lift, and more pitching
moment. They would possibly be good on a canard if flaps were mounted on the
main wing.
Mark Muller
mul...@vibes.ae.utexas.edu
John R. Johnson
1. What do leading edge slats do ...
2. Why don't canards land as slowly as they can?
1. Leading edge slats, whether they are fixed or moveable, assist the airflow
in making the critical turn about the leading edge. As the angle of attact
increases, the stagnation point moves lower and lower around the leading
edge. Anything that makes it easier for the air to flow up and around the
leading edge will delay the onset of forward separation, or stall. Slats
direct and energize this flow and generally increase lift by allowing the
angle of attact to increase with an approximatly linear increase in lift
with angle, to higher values. For example, instead of stalling at 10
degrees
you could go up to 13 or 14 without a stall. Of course drag is increasing
rapidly all this time. Max lift is given with a combination of flaps and
slats, albeit at the cost of extreme drag. Vis a vis the modern jet
airliners 50 percent wing disassembly on approach! :^)
I would not like to predict the low speed characteristics of canards with
these additions without a LOT of testing.
2. In most canard designs, maybe in ALL canard designs, both surfaces are
lifting surfaces. That is what gives you the increase in efficiency in
canard designs. In a normal configuration the tail produces a down load
which has to be supported by the wing and INCREASES the effective weight
of the airplane by the amount of down load. That is why most airplanes
are a little faster when they are loaded toward the aft CG limits! In
the canard there is NO downforce to increase effective weight. Since
both surfaces are lifting surfaces, if the forward surface stalls first
the angle of attact decreases, unstalling the aircraft. If the after
surface stalls first the angle of attact increases repidly, stalling
all surfaces, and it may become impossible to recover from the stall
while remaining in the air. This makes stall recovery somewhat painful
under most circumstances. At the same time, when the forward surface
stalls, with the after surface still flying, the result is usually a
rather abrupt pitchdown. If you were in a landing flare when this
happened you would have a very astonished look as you slid down the
runway on your figurative schnozzola. Therefore, we normally set the
landing speeds and incidences such that both surfaces are flying at
touchdown. This means that you land above stall speed. Therefore you
land somewhat faster than absolutely necessary, were it a conventional
design. In practice, this difference is NOT all that great. Just
remember, if you cannot stall the airplane, you cannot make a "full stall"
landing.
JOhn.
ChaniK
Having been sued a couple times, he won't even give advice for mods to
his own line of kit planes anymore.
Richard Barnett
writes:
(Snip)
>
>Burt Rutan put together a STOL canard design called the Grizzly.
>It had 4 Fowler flaps: 2 on the wings, 2 on the canard.
>They were serious flaps extending for 55% of the
>chord. Possibly he got around the pitch problem by using the 4
flaps.
>There was even a proposal made to put the Griz on amphibious floats!
>It was flying in 1982.
>--
>Roger Bleier
>tn...@acad1.alaska.edu
>Sitka, Alaska
It's a NEAT looking airplane! You can currently see it at the EAA
Air Adventure Museum (along with the prototype VariEze, etc.), for
those of you who haven't been there yet. I HIGHLY recommend a visit!
Rusty
Paul Neelands
>From: Mark Brian Muller <mul...@vibes.ae.utexas.edu>
>Subject: Re: No flaps on canards?
>Date: 25 Aug 1995 15:57:33 GMT
>ran...@majik35.ColumbiaSC.NCR.COM (Randy Smith) wrote:
>Mark Muller
>mul...@vibes.ae.utexas.edu
Beware here.
1.
Leading edge flaps usully interfere with extensive laminar flow thus destroying
the efficiency that is the hallmark of the canard design. It is extremely
difficult to use a natural laminar flow airfoil which is laminar over 60 - 70%
of the foil with any sort of flow disruption near the leading edge.
2.
Although leading edge slats clearly improve pitching moments, they do so
at the risk of a much sharper stall. Placing leading edge slats on a canard
could easily change the usual canard stall "pitch buck" behaviour into serious
uncontrollable pitch down if the slat equipped canard were to stall.
3.
Any increased angle of attack or increased lift on the canard places the main
wing closer to stall and subsequent aircraft deep stall. See Nat Puffers tests
on Cozy or the Velocity deep stall discussion earlier.
4.
Placing flaps on a canard aircraft is exceedingly difficult. So far it has
consumed roughly 1000 hours of simulation time on my reasonably
speedy PC with only the outline of a solution so far.
Paul Neelands
Building a Cozy IV
JHocut
canard aircraft, I too am building a Cozy.
I read Nat Puffer's study with great interest. One question though
concerning the unrecoverable stall. As far as I know, a "deep stall" has
only been encountered with the CG way out of the aft limit. As long as
the CG is within limits, wouldn't a stall be "normal" in that you recover
by lowering the angle of attack? In other words, if the canard were sized
to have enough authority with flaps deployed, would there REALLY be a
problem with stalls as long as the CG remained within limits?
Jim
Mark Y. deLevie
: to have enough authority with flaps deployed, would there REALLY be a
: problem with stalls as long as the CG remained within limits?
Yes. There would then be too much canard authority when the flaps are
stowed... in other words, you could stall the main wing before you stall
the canard.
Mark deLevie
Paul Neelands
>From: jho...@aol.com (JHocut)
>Subject: Re: No flaps on canards?
>Paul, I'd love to hear more about your studies of putting flaps on a
>canard aircraft, I too am building a Cozy.
>I read Nat Puffer's study with great interest. One question though
>concerning the unrecoverable stall. As far as I know, a "deep stall" has
>only been encountered with the CG way out of the aft limit. As long as
>the CG is within limits, wouldn't a stall be "normal" in that you recover
>by lowering the angle of attack? In other words, if the canard were sized
>to have enough authority with flaps deployed, would there REALLY be a
>problem with stalls as long as the CG remained within limits?
>Jim
>jho...@aol.com
Paul
The work on putting flaps on a canard has been going on for about 2 years.
I expect several more before I have clear theoretical answers.
Some quick tidbits.
1. If at any point in the speed and loading range of the aircraft
the canard has a higher stalling angle of attack than the main
wing. You have a deep stall problem.
2. Point 1 is not quite true however, a bit closer is that the
loading on the canard must always be higher in all possible
situations than that of the main wing. The loading here is
really just used to move the canard further up it's lift/angle
of attack curve.
3. Given the same conditions as above, if the lift vs angle of attack
slope of the canard is ever greater than the main wing, the
aircraft becomes dynamically unstable.
ie. A pitch up will cause the canard to move up the lift curve
more than the main wing causing more pitch up.
4. Stability is usually acheived for a canard by having a very low
lift/alpha curve on the canard and a fairly steep one for the main
wing. Thus on pitchup the canard lift will not increase as much
as the main wing. Thus restoring the aircraft to approximately
level flight.
5. This is now getting close to the core of the problem. Adding flaps
causes the lift/angle of attack curve to steepen. Putting flaps
on both the canard and the main wing causes both surfaces to have
steep lift/alpha curves.
6. But stability for a canard is really the difference between the
two curves. Thus steepening the lift/alpha curves reduces the margin
between the two. Eventually you run out of room to manuever so
to speak.
Sorry about the run on here.
One solution is to try a movable canard ala Starship. The usual
result of this is only a small increase in stability and the
Starship flaps really only serve to increase drag and steepen the
descent. (A nice side effect though.)
Another solution is a rotatable canard. Unfortunately someone
tried this on a LONGEZ and got into the unstable area where the
canard slope is steeper than the main wings slope and was killed
on the first flight. There are serious structural problems also.
At present I'm working on the problem using Panel Method
computational aerodynamics to get close to potential solutions
and then switch to Euler methods. All this stuff is coupled into
an optimization program that searches for global optima. It runs
more or less continually by itself on a dedicated machine. It's
unclear why I'm doing this, except that I would like a better
canard aircraft to fly.
This seems like a good place to stop for now.
Paul Neelands
Building a COZY IV
Charles K. Scott
of the faster fabric covered airplanes and find out what makes them go
so fast. The answer was pretty simple actually: tiny wings and huge
engines. But many of them had some pretty clever speed mods on them
which I took pictures of.
The Monocoupes were there as well as the "Mr. Mulligan". Both
airplanes have a similar wing configuration to my Christavia; a high
wing attached to the fuselage above the cockpit and supported by a
V-strut. The attachment of the V-strut was my area of focus because it
offers several connections that are in a high drag area. Especially
where the two streamline tubes attach out at the wing. The Monocoupes
dealt with this connection by making a real nice looking fairing for
each tube. Mr. Mulligan took a different tack. The designer built a
large fairing that was like a blister starting in front of the first
tube and carrying all the way back past the second tube and tapering to
a point at the trailing edge of the wing. This meant that the aileron
had to have a part of the blister on it, and it had to interact with
the fairing on the wing every time the aileron moved. The whole point
appeared to be to offer a faired surface that was 90¡ to the tube since
any angle less than 90¡ on an airplane increases drag. (a side note:
this is why the F4U Corsair has no wing fairing at the wing to fuselage
junction, the inverted gull wing configuration allows a clean 90¡
juncture)
I've discussed this before and I'm still curious. Would anyone like to
comment on the differences in technique for fairing this area? One
notion has it that the Mr. Mulligan fairing, while effective, offers
more overall drag due to it's large size. The other that the reduction
in turbulence makes up the difference and then some.
In either case, I'm going to have to modify the wing slightly to make
the fairing effective. I'll have to glue plywood to the bottom of the
wing where this fairing will be because in flight, the fabric tends to
push up between the ribs which will make a gap between the fairing and
the fabric causing turbulence in this high lift area. The plywood will
prevent that from happening. I'll need to cover about three ribs
total.
Does anyone have any opinions?
Corky Scott
AlFITZ
Charles...@dartmouth.edu (Charles K. Scott) writes:
>
>In either case, I'm going to have to modify the wing slightly to make
>the fairing effective. I'll have to glue plywood to the bottom of the
>wing where this fairing will be because in flight, the fabric tends to
>push up between the ribs which will make a gap between the fairing and
>the fabric causing turbulence in this high lift area. The plywood will
>prevent that from happening. I'll need to cover about three ribs
>total.
>
>Does anyone have any opinions?
>
>
Sure I do, but not about this.
Al Fitzgerald
John R. Johnson
of maintaining stability on canards with changes in lift as from flaps.
Thank you for the excellent post. You did a good job of indicating some of
the many factors that enter into the problem. It is NOT a trivial task to
just add some flaps on canards. Stability must be considered at all loadings
and in all flight regimes. Stability must also be considered for the special
cases involved when something doesn't work right, or breaks. For example,
what would happen if the flaps extended on the forward surface, but failed
to extend on the after one? It would scare ME. :^)
John
John R. Johnson
This is a very judgemental area. Which factor is more significant
profile drad of the faring surface, or interference drag from the
acute angle connections? I could hazard lots of guesses, some of
them even somewhat educated. They would still be guesses until you
put samples of each into a wind tunnel and compared them. I would
be really interested in seeing the resulting data.
John